Merck Serono spends the largest proportion of its sales on developing new drugs, according to Business Monitor International’s Pharmaceutical Research Investment Index (PRII) for the first quarter of 2010.

The Geneva-based drug manufacturer spent $377m on new drug development, equivalent to 20% of its sales.

Its R&D costs increased 11% compared to the same period a year previously, attributed to a large number of late-stage clinical trials.

BMI’s PRII found that many large pharmaceutical firms, GlaxoSmithKline and Pfizer included, have reduced R&D expenditure in order to maintain profit margins.

However, Danish drug manufacturer Novo Nordisk increased their R&D spend by 22%.